1. Field of the Invention
The present invention relates to a die for press brake having a construction in which many flat plate-shaped die elements are laminated.
2. Description of the Related Art
FIG. 9(A) shows a general die for press brake. The die for press brake generally denoted by reference numeral 1 has an upper die 2 and a lower die 3.
In the lower line portion of the upper die 2, a bending blade 2a is formed, and in the upper line portion of the lower die 3, a V-groove 3a is formed.
When a work W1, which is a product, is bent, a raw material is held between the upper die 2 and the lower die 3, and pressing is performed, as shown in FIG. 9(B).
Such a die for press brake has been disclosed, for example, in Japanese Patent Laid-Open Publication No. 2000-140941 (Patent Document 1).
Also, a construction in which the die for press brake is divided has been disclosed in Japanese Patent Laid-Open Publication No. 2001-205338 (Patent Document 2) and Japanese Patent Laid-Open Publication No. 2001-1048 (Patent Document 3).
When the above-described conventional die for press brake is used to bend a work having a curved portion B1 in which the radius of curvature changes continuously from a curved portion R1 having a small radius of curvature to a curved portion R2 having a large radius of curvature as in the case of a work W2 shown in FIG. 10, a plurality of bending operations performed along a plurality of bend lines ML must be repeated.
However, even if the above-described bending operations are performed a plurality of times, the curved portion B1 is a collection of straight-line bend portions, and a continuous curved surface cannot be formed.
An object of the present invention is to provide a die for press brake in which a curved surface having a continuously changing radius of curvature can be formed by one pressing operation.